Jacks are used to apply loads or forces in various applications. Typically, a jack is used to apply a push (compressive) or pull (tensile) force to an object. In a particular application, jacks can be used to test the load-bearing capacity and/or stability of piles or other structures. Such structures can be manufactured in various configurations and from various materials. Engineering piles, for example, can be made from wood, concrete, steel, or other building materials known in the art. Such structures can be used for various purposes. Engineering piles, for example, are often driven into the ground, or created by pouring concrete in a formation formed in the ground, to form a foundation for buildings, bridges, or other structures. The jacks can be located under, on top of, or within, the pile and apply a load upward on the pile and/or downward on to the ground beneath the pile, a section of the pile below the jack, or the top of the pile. Regardless of the application, it is often useful to know with some degree of accuracy the load or force applied by a jack.
When a hydraulic jack is used, it is known to measure the pressure of hydraulic fluid in the hydraulic jack and to use such measure of the pressure of the hydraulic fluid and the surface area of the jack effectively normal to the direction of the force in contact with the hydraulic fluid to calculate the load applied by the hydraulic jack. The load is typically the pressure of the hydraulic fluid times the surface area effectively normal to the direction of force being applied by the hydraulic fluid. As an example, for a jack having a cross-sectional area, A, in contact with the hydraulic fluid perpendicular with the direction of the force to be applied by the jack, the force can be calculated as F=P·A, where P is the pressure of the hydraulic fluid. However, this method of measuring force can be temperature sensitive because the volume and pressure of the hydraulic fluid will often vary with temperature. Further, this method of measuring force does not account for certain sources of friction, such as friction between the piston and the jack cylinder. Thus, the true load applied by the hydraulic jack can easily differ significantly from the load calculated from the measured pressure of the hydraulic fluid.